The neuropsychological study of twins with psychiatric disorders has rarely been attempted. In the present study, groups of monozygotic twins whose members are both normal, whose members are both schizophrenic, and whose members are discordant for schizophrenia (i.e., one member is normal and one member is schizophrenic) will be assessed with a complete neuropsychological battery. Included tasks that assess motor functioning, attentional skills, memory abilities, higher level abstract problem solving, and basic language and visual spatial functions. Also tests of dichotic listening with both neutral and affectively charged words were administered to assess laterality and emotional responsivity. By the use of matched pair design in which both genetic and early social environment is more or less completely controlled, as well as the experience of twinship itself, it is hoped that the pattern of deficits found will elucidate impairment in schizophrenic disease.